1. Field of the Invention
The invention relates to a system for recording and/or reproducing information, comprising
a magnetizable medium provided with a track pattern comprising
buried servotracks of a first type containing a first signal, and
buried servotracks of a second type containing a second signal,
which servotracks extend substantially in a longitudinal direction and which track pattern, in a transverse direction perpendicular to the longitudinal direction, alternately comprises a servotrack of the first type followed by a servotrack of the second type, and an apparatus comprising
a magnetic head unit comprising a plurality of heads at different positions in the transverse direction,
means for moving the medium relative to the magnetic head unit in the longitudinal direction,
an actuator for moving the magnetic head unit relative to the medium in the transverse direction, and
a control unit for controlling the actuator, which control unit is adapted to generate a position signal based on the difference between the signals of two heads.
The invention also relates to a medium for such a system.
The invention further relates to a magnetic write head comprising a head face with a longitudinal direction in which a magnetizable medium is movable relative to the magnetic write head, and a transverse direction oriented transversely to the longitudinal direction, and further comprising a structure of integrated write units, which structure terminates in the head face, which write units are disposed adjacent one another in the transverse direction, extend substantially in the transverse direction and each have a write gap.
The invention also relates to an arrangement comprising such a magnetic write head and means for scanning a magnetizable medium with the head.
2. Description of the Related Art
Such a medium, such a system and such a magnetic write head are known from WO 96/30897-A2. The known medium is a magnetic tape on which seven servotracks have been written by means of the known magnetic write head, the signal in the first servotrack being in phase with the signal in the third, the fifth and the seventh servotrack and the signals in the second, the fourth and the sixth servotrack being in phase opposition to the signals in the first, the third and the fifth servotrack. By means of an apparatus forming part of the known system it is possible to write information signals over the servotracks on the magnetic tape thus formatted. For this purpose, the apparatus comprises a magnetic head unit having four heads and means for moving the magnetic tape past the magnetic head unit in a longitudinal direction. The known apparatus further comprises an actuator for positioning the magnetic head unit in a transverse direction and a control unit for controlling the actuator. The control circuit comprises a comparator for generating a position signal based on the difference between the signal supplied by a first head and the signal supplied by a second head. The magnetic head unit follows the servotracks on the magnetic tape on the basis of the position signal. A disadvantage of the known system, the known medium and the known magnetic write head is that after the whole magnetic tape has been written or read the magnetic tape is to be rewound in order to return it into its initial position. Another disadvantage of the known system is that only one half of the number of heads supplies information about the position of the servotracks relative to the magnetic head unit.
It is an object of the invention to provide a system, a medium, a magnetic write head and an arrangement of the types defined in the opening paragraphs, by means of which it is possible to achieve a high accuracy of positioning the magnetic head unit relative to the track pattern on the medium and by means of which it is possible to read and/or write the information from/on the track pattern in an even number of passes. To this end, the system in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,
the bands of the first type comprising N1 servotracks having a first typical width W1,
the bands of the second type comprising N2 servotracks having a second typical width W2, which complies with
N2=2, 4, 6 etc. and W2=(k+xc2xd)W1 or
N2=1, 3, 5 etc. and W2=2 k.
where k=1,2 etc.,
and the center-to-center distance p between the heads complies with the relationship p=nxc2x7W1, where n=2, 4, 6, . . . etc.
By means of the measures in accordance with the invention it is achieved that the information can be read from and/or written on the track pattern in an even number of passes of the magnetic head unit relative to the medium and the position signal is immune to tolerances in the servotrack width and to amplitude differences between the first signal and the second signal. This immunity is achieved in that there are always at least two heads disposed on a boundary between two adjacent servotracks and in that these heads read a servotrack of the same one type by means of their facing parts and in that they read a servotrack of the other type by means of their parts which are remote from one another. The above-mentioned tolerances influence the signals read by means of these heads to the same extent, as a result of which these tolerances are cancelled in the actuator drive because this drive is based on the difference between the signals read by the relevant heads. If the apparatus is required to have a write capability, the heads are adapted to read servosignals and write information signals at the same time.
An embodiment of the system in accordance with the invention is characterized in that the medium has at least one servotrack having a width of at least nxc2x7W1. Owing to these measures one head can be disposed wholly on the nxc2x7W1 wide servotrack during all passes, thereby enabling this head to be used for reading a speed signal representative of the speed of the medium with respect to the magnetic head unit in the longitudinal direction. Owing to said measures the magnetic head unit need not be positioned accurately in the transverse direction in order to generate the speed signal. This simplifies starting of the system in accordance with the invention.
The medium in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,
which bands of the first type comprising N1 servotracks having a first typical width W1,
the bands of the second type comprising N2 servotracks having a second typical width W2, which complies with
N2=2, 4, 6 etc. and W2=(k+xc2xd)W1 or
N2=1, 3, 5 etc. and W2=2k.W1,
where k=1, 2 etc.
The medium in accordance with the invention can be used in the system in accordance with the invention with the advantages outlined above.
An embodiment of the medium in accordance with the invention is characterized in that N2=1 and k=1. By means of an apparatus comprising, for example, three heads disposed at a center-to-center distance of at least 2xc2x7W1 and having a recording width of approximately W1 this track pattern can be provided wholly with information tracks in an even number of passes. For example, if N1=1 this can be effected in two passes. The track pattern can be repeated several times in the transverse direction of the medium, as a result of which the magnetic head unit can inscribe a following track pattern with information after a displacement in the transverse direction. In a preferred embodiment N1=7, three of such track patterns are juxtaposed in the transverse direction and are spaced by a servotrack of 2xc2x7W1 width, and a band of the first type adjoins a servotrack having a width of 1.5xc2x7W1 adjacent a servotrack having a width of at least 9xc2x7W1. By means of an apparatus having eight heads disposed at a center-to-center distance of 8xc2x7W1 and a recording width of approximately W1 or less it is possible to write 64 information tracks over this track pattern in eight passes. An advantage of this embodiment is that each of the eight passes can be identified on the basis of the servosignals read by the heads. For example, in the first pass the signal of the second head is in phase with the signal of the first head and in the second, the third etc. through the eighth pass the signal of the second, the third etc. through the eighth head is in phase opposition to the signal of the first head. This makes it possible to preclude that the servosystem, for example after being subjected to an external mechanical shock, locks to another pass, where the apparatus continues writing.
An embodiment of the medium in accordance with the invention is characterized in that N2=2 and k=1. For example, if N1=3 it is possible to write in four passes twelve information tracks over this track pattern by means of an apparatus comprising three heads disposed at a center-to-center distance of 4W1 and having a recording width of approximately W1 or less.
Preferably, the above-mentioned embodiment is such that N1=11 and a band of the first type adjoins a servotrack having a width of 1.5xc2x7W1 and adjoining a servotrack having a width of at least 5xc2x7W1. With this preferred embodiment said track pattern can be inscribed with 32 information tracks in four passes by means of an apparatus comprising eight heads disposed at a center-to-center distance of 4W1 and having a recording width of approximately W1 or less. In the case of this preferred embodiment six heads are always disposed on a boundary between two adjacent servotracks, as a result of which six of the eight heads supply information about the position of the magnetic write head with respect to the track pattern. Since in this embodiment a large number of heads contribute to the generation of the position signal a high degree of robustness is achieved. This enables a satisfactory tracking to be obtained even if a part of the servotracks is unreadable. Two heads are always situated wholly on one servotrack, as a result of which these heads can supply information about the phase of the servosignal and the speed of the medium relative to the magnetic head unit. An advantage of this embodiment is that each of the four passes can be identified on the basis of the servosignals read by the heads. Thus, in the first pass the signal of the second head is in phase with the signal of the first head and in the second pass the signal of the second head is in phase opposition to the signal of the first head. In the third pass the signal of the fifth head is in phase opposition to the signal of the first head and in the fourth pass the signal of the fifth head is in phase with the signal of the first head. This makes it possible to preclude that the servosystem, for example after being subjected to an external mechanical shock, locks to another pass, where the apparatus continues writing.
An embodiment of the medium in accordance with the invention is characterized in that the first signal and the second signal each contain the same fundamental and the first signal and the second signal are in phase opposition to one another. By means of these measures it is achieved that the signal read by a head is zero if it is centered with respect to a boundary line between two servotracks. This is advantageous because, as a result of this, differences in sensitivity between the heads have substantially no influence on the generation of the position signal and because a measurement signal which varies about zero makes it possible to implement a servosystem which is accurate and highly insensitive to offsets in the control unit.
The invention is particularly advantageous if the medium is a tape-like medium wound on a reel hub and accommodated in a housing of a cassette. With such a cassette the position of the medium relative to an apparatus with which the cassette cooperates is generally inaccurate because a tape-like medium is slack and this position is also determined by the housing of the cassette. In addition, the dimensions of a tape-like medium in the transverse direction can vary owing to expansion or contraction as a result of the absorption of moisture or release of moisture by the medium. The measures in accordance with the invention yet ensure an accurate position of the magnetic head unit with respect to the medium, as a result of which high-density information storage is possible on the medium. Moreover, the medium in such a cassette is not fully protected against the ingress of dust and dirt from the environment and there is mechanical contact between the medium and the magnetic head unit, which may give rise to scratches. As a result of dust, dirt or scratches a part of the servosignals may be disturbed or completely unreadable at some locations. The measures in accordance with the invention mitigate the effect of dust, dirt and scratches on the tracking.
The magnetic write head and the arrangement in accordance with the invention are characterized in that
the structure comprises a group of at least two bands of a first type, which are separated by a band of a second type,
the bands of the first type adjoin a write gap at their sides remote from the band of the second type,
the bands of the first type have N1 write gaps having a first typical width W1 and
the band of the second type has N2 write gaps having a second typical width W2, which complies with
N2=2, 4, 6 etc. and W2=(k+xc2xd)W1
or
N2=1, 3, 5 etc. and W2=2k.W1,
where k=1, 2 etc.